Predrag R. Bozic

Evaluation of the Field Tests of Flexibility of the Lower Extremity: Reliability and the Concurrent and Factorial Validity

Bozic, PR, Pazin, N, Berjan, BB, Planic, NM, and Cuk, ID. Evaluation of the field tests of flexibility of the lower extremity: Reliability, and the concurrent and factorial validity. J Strength Cond Res 24(9): 2523-2531, 2010-The purpose of this study was to evaluate the standard field tests of flexibility of the lower extremity through their (a) intratrial and test-retest reliability, (b) concurrent validity with respect to a high-precision 3D system for kinematic recording, and (c) factorial validity. Physically active men (n = 84) were tested over 2 separate sessions by means of standard simple devices (kinanthropometry, ruler, and protractor) on the following flexibility tests: leg raise in a supine position, hip abduction test, single-legged knee bend (SLKB), sideward leg splits (SdLS), sit and reach (SR), sideways leg splits, and lengthwise leg splits. Additionally, 17 participants were simultaneously tested by means of a laboratory 3D kinematic analysis system. Most of the tests demonstrated high intratrial and test-retest reliability and concurrent validity. The exceptions were SLKB and SR tests that revealed not only a somewhat lower reliability but also a lower concurrent validity. For estimation of factorial validity, we applied a principal component analysis of the intercorrelations among the evaluated flexibility tests that revealed a single extracted principal component. Strong mutual relationships among them also suggest that very few of them, if not a single one, should be applied within the standard batteries of physical performance tests. We particularly recommend using SdLS over the most frequently used SR not only because of its relatively high reliability and validity but also because of its postural properties. Finally, we conclude that most of the standard field tests of flexibility of the lower extremity based on using inexpensive field equipment could be both reliable and valid and, therefore, justified for use in routine testing.

Tests of Muscle Power Output: The Role of Body Size

The effect of body size on the output of the tests of directly assessed muscle power has been mainly ignored in the applied research. We hypothesized that the muscle power output would reveal a positive relationship with body size closely in line with the theoretical predictions, as well as that the strength of the studied relationship could justify standardized normalization procedures applied in routine testing. Male physical education students (n = 111) were evaluated in 10 standard tests of direct assessment of muscle power output. A standard allometric relationship P = A SB was applied to assess the relationship between the tested power output P and selected indices of body size S ( B = allometric exponent; A = parameter). The correlation coefficients obtained between the tested power output and body size ranged within 0.21 - 0.56 for body mass and 0.10 - 0.49 for body height. The mean (SD) values of the allometric exponents B obtained with respect to body mass and body height were 0.55 (0.15) and 1.15 (0.62), respectively. This relationship proved to be strong enough to merit applying a standard normalization. The normalization method should be based on body mass as a preferred index of body size, while the allometric exponent could correspond to the theoretically predicted one (i.e., B = 0.67).

Evaluation of a Composite Test of Kicking Performance

Abstract Berjan Bacvarevic, B, Pazin, N, Bozic, PR, Mirkov, D, Kukolj, M, and Jaric, S. Evaluation of a composite test of kicking performance. J Strength Cond Res 26(7): 1945–1952, 2012—The aim of this study was to evaluate the reliability and sensitivity of variables for the direct assessment of kicking performance in young soccer players. One hundred and six elite young soccer players were divided into 4 age groups (12–15 years). Absolute error (AE), variable error (VE), and constant error (CE) were evaluated as the variables of kicking accuracy, whereas the kicking velocity variables involved the maximum ball velocity (BVmax) and the ball velocity during accurate kicks (BVacc). Results suggested low-to-moderate reliability of the kicking accuracy (intraclass correlation coefficient [ICC] = 0.00–0.67) and high reliability of the kicking velocity variables (ICC = 0.87–0.94). Regarding the sensitivity, most of the variables detected the differences both between the dominant and nondominant legs and among the age groups. Because the evaluated variables should have a property of face validity, the findings obtained generally suggest that AE (and perhaps VE, as the measures of kicking accuracy) and both BVmax and BVacc (as the measures of kicking velocity) could be used within a routine composite test of kicking performance in young elite soccer players. Further development of the evaluated composite test of kicking performance could be based on the involvement of other kicking techniques and on testing the athletes of different ages, levels of skill, or sport specialization.

Alternating consecutive maximum contractions as a test of muscle function.

Bozic, P, Suzovic, D, Nedeljkovic, A, and Jaric, S. Alternating consecutive maximum contractions as a test of muscle function. J Strength Cond Res 25(6): 1605-1615, 2011—Although regularly used, the standard strength test (SST) is known to have several shortcomings, such as being based only on sustained maximum forces, and on a relatively large number of trials that expose the tested muscle to rapid fatigue. The purpose of this study was to evaluate alternating consecutive maximum contractions (ACMCs) as a test of the muscle function through its comparison with SST. Twenty-four participants performed both the externally paced isometric ACMC (i.e., series of consecutive maximum force exertions in 2 directions) and SST of the knee extensor and flexor muscle. The derived variables of both tests included the knee extensor and flexor peak forces (PFs) and their maximum rates of development. Movement speed and muscle power output were also assessed through standard maximum performance tests. Both ACMC and SST revealed on average high intratrial (intraclass correlation coefficient [ICC] > 0.80) and moderate-to-high test-retest reliability (ICC > 0.60), and significant (p < 0.05) positive relationships among the PFs and their rates of development of the tested muscles. The variables of both tests also suggested on average moderate correlations with the maximum performance tests. Finally, ACMC variables revealed relatively stable values across a wide range of frequencies including the ‘self-selected’ one. Although some properties of ACMC could be similar to SST, the important comparative advantages of ACMC could be relatively low and transitional maximum forces exerted, and fewer trials needed for testing 2 antagonistic muscles. Although further research is needed, particularly concerning the external validity and generalizability, we conclude that the ACMC represents a test of muscle function that could be applied either as an alternative or complementary test to SST.

WHO European Childhood Obesity Surveillance Initiative in Serbia: a prevalence of overweight and obesity among 6-9-year-old school children.

Abstract Background: The World Health Organization (WHO) European Childhood Obesity Surveillance Initiative (COSI) is a public health program established in order to understand the progress of the obesity epidemic in young populations and gain inter-country comparisons within the European region, yet the data from a number of East European countries, including Serbia, were not available then. Therefore, the main aim of this cross-sectional study was to collect data about the prevalence of overweight and obesity among 6–9-year-old school children in Serbia according to the standardized protocol during the Fourth COSI Implementation Round. Methods: From September 2015 to November 2015, 5102 first- and second-grade primary-school children (age 7.7±0.6 years) were assessed for weight, height, and body mass index (BMI) in 14 Serbian school districts. Results: The prevalence rates of obesity, as calculated using the International Obesity Task Force (IOTF) cut-off points, vary across different age groups, with the lowest obesity rates reported in 7-year-old boys (6.2%), while the highest obesity prevalence rates were observed in 6-year-old boys (9.7%). In addition, being overweight was strongly associated with poor local community development and lower level of urbanization. The overall prevalence of overweight (23.1%, including obesity) and obesity (6.9%) in Serbian primary-school children seem to be comparable to rather high rates previously reported in other countries participating in the COSI program, indicating an obesity epidemic in Serbian children. Conclusions: This surveillance system should be regularly implemented throughout Europe, providing comparable data on rates of overweight/obesity in primary schools that might drive prudent actions to reverse the pandemic trend of childhood obesity.

Evaluation of novel tests of neuromuscular function based on brief muscle actions.

Abstract Bozic, PR, Celik, O, Uygur, M, Knight, CA, and Jaric, S. Evaluation of novel tests of neuromuscular function based on brief muscle actions. J Strength Cond Res 27(6): 1568–1578, 2013—Although widely used, the standard strength test (SST) is known to provide moderate correlations with functional measures, while being based on sustained maximum forces and a relatively large number of trials. The aim of this study was to compare the concurrent (with respect to SST) and external validity (with respect to the standard balance and maximum power output tests) of 2 alternate tests of neuromuscular function based on brief isometric actions. The first test provides a slope between the rates of torque development (RTD) and peak torques (T) measured from a number of consecutive rapid actions performed across a wide range of T levels (brief force pulses, BFP). The second test (alternating consecutive maximum contractions, ACMC) provides T and RTD from multiple cycles of rapid alternating maximum actions of 2 antagonistic muscle groups. The results obtained from 29 young and healthy subjects revealed moderate-to-high concurrent validity of ACMC (median r = 0.56, p < 0.05) and its similar, if not higher external validity than SST. Conversely, both the concurrent and external validity of BFP seemed to be relatively low (r = 0.23, p > 0.05). Because ACMC could also have advantage over SST by being based on somewhat lower and transitional muscle forces exerted and fewer trials are needed for testing 2 antagonistic muscles, the authors conclude that ACMC could be considered as either an alternative or complementary test to SST for testing the ability for rapid exertion of maximum forces. Conversely, BFP may offer a measure of the neuromuscular system “as a whole” that is complementary to SST by providing outcomes that are relatively independent of muscle size and function.